The interior of an automobile is desirably insulated from sounds, which may be transmitted through the frame and body of the automobile. These sounds typically originate from the tires as they interact with the road surface, from external wind, or from the operation of the engine and other mechanical parts of the automobile. These sounds have frequencies ranging from a few Hertz (Hz) up to several thousand Hz.
While those skilled in the art recognize that a sound absorber is most effective at a thickness corresponding to one fourth of the wavelength of the frequency of sound to be absorbed, practical considerations of space and cost may limit the actual thickness of the insulating composites which can be employed. Acoustic blankets are designed with a variety of materials and configured to be installed against surfaces of structural panels of an automotive vehicle. The insulating blankets, or pads, serve to dampen, block, absorb or attenuate unwanted road noise and external sounds. Most commonly, these blankets are comprised of recycled textile fibers formed into a material called shoddy. In some instances, foam materials may be used.
With shoddy used in automobiles, a practical upper limit of insulating composite thickness is often thought to be approximately 25 mm (one inch) since the shoddy tends to be dense and heavy. Therefore, it is known in the art to apply an acoustical insulating barrier, sometimes called a heavy layer or viscoelastic layer, to the shoddy material for overall improved efficiency of sound reduction. Such a barrier material may double as carpeting attachment or may be included in the carpet fabrication. See, for example, U.S. Pat. Nos. 4,056,161; 4,966,799; 5,266,143; 5,068,001; and 6,109,389, the disclosures of which are hereby incorporated in their entirety.
Asphalt compositions, which are highly filled with dense inert powder (usually of a mineral nature) are applied in a molten state as disclosed in U.S. Pat. No. 3,429,728. Thermosetting resins like melamine, phenol-aldehydes, and urea resins are taught in U.S. Pat. No. 3,536,557, and dense filled vinyl plastisols are disclosed in U.S. Pat. No. 4,035,215. A variety of thermosetting and thermoplastic barrier materials are used in U.S. Pat. No. 4,131,664 to create the heavy or dense barrier layer. Also, a polymeric sound blocking material is disclosed in U.S. Pat. No. 3,424,270. All patents disclosed are hereby incorporated by reference in their entirety.
A drawback to the acoustical dampening materials disclosed in many of these patents is that they contribute significant weight to the vehicle. Those skilled in the art of acoustics and insulation understand that the best sound barrier is often times a heavy, dense material such as lead sheeting. However, a few pinholes or cracks can compromise even a thick or heavy sound barrier.
In lieu of sound barriers, sound absorbers, have been used in the art. Sound absorbers typically are significantly less dense than barrier materials, and may be porous. As a result, their acoustic performance is less affected by pinholes or cracks. In addition to absorbing sound energy, other mechanisms of reducing the perceived sound are to dampen and to block the sound waves. Although structural insulation requirements differ from automotive requirements, the technical learnings of one apply directly to the other.
In a final analysis of the final product, the actual physical mechanism of sound reduction (blocking or absorption) does not matter. The human ear or even a microphone cannot tell if a transmitted sound has been partially blocked or partially absorbed. In applications with numerous penetrations of the acoustic and structural panels, as in the firewall of an automobile, a sound-absorbing material may actually outperform a barrier material since the gaskets around the penetrations must be nearly perfect for the barrier material to be highly efficient in blocking the incident sound.
Routinely in the manufacture of vehicles, fibrous panels are die cut and/or molded under heat and pressure to impart a shape-sustaining contour to uniquely conform to the sheet metal of each make and model of vehicle. The molding operation can involve a heated die and cold material, or the acoustic material itself is heated and then pressed in a cold die.
Criteria in the manufacture and use of sound absorbing and blocking composites, pads, batts, or blankets have been the cost of the textile raw material itself, the cost of processing the materials into heavyweight nonwoven blankets, and the ease by which such blankets can be custom-molded to fit precisely against the structural panels of the vehicle. Other technical parameters of importance have been the acoustical properties of such fibrous nonwovens, their weight, and their durability over prolonged service during which time they may be subjected to wide variations in heat and humidity and quite possibly exposure to solvent or water-based adhesives.
Reducing the size and weight of vehicles has long been known to be effective in improving gas mileage. However, there have not heretofore been economically viable options for incorporating lighter-weight acoustic insulation materials while retaining the expected level of sound-insulating performance. The present invention offers nonwoven structures as a lighter alternative for acoustic insulation, providing a reduced, controlled airflow therethrough.
It is also known in the textile industry to produce fire-retardant fabrics for use as upholstery, mattress ticking, panel fabric, and other items. Such items are formed of natural or synthetic fibers, and then treated with fire-retardant chemicals. Conventional fire retarding chemicals include halogen-based and/or phosphorous-based chemicals. In approaches to render fabrics semi-permanently to permanently fire-retardant, whereby the fire-retardant chemical is reacted with the cellulose or protein functionalities of natural fibers, U.S. Pat. No. 2,832,745 discloses amidophosphates reacting with trimethylol melamine to form a thermosetting resin within the textile fiber. U.S. Pat. No. 4,026,808 reports on the use of a phosphorous containing N-hydroxy-methyl amide and tetrakis(hydroxymethyl)phosphonium chloride.
In what might be best described as a coating application, U.S. Pat. No. 3,955,032 reports a process using chlorinated-cyclopentadieno compounds and chlorobrominated-cyclpentadieno compounds, either alone or in combination with metal oxides, suspended in a latex medium and cured to render natural and synthetic materials and blends of the same fire-retardant. Similarly, in U.S. Pat. No. 4,600,606 a method of flame retarding textile and related fibrous materials is reported, which relies upon the use of a water-insoluble, non-phosphorous containing brominated aromatic or cycloaliphatic compounds along with a metal oxide to treat fabrics for protection against splashes of molten metals or glass. In yet another example of a dispersion of phosphorous-containing compounds and metal oxides in latex, U.S. Pat. No. 4,702,861 describes a flame retardant composition which, upon exposure to elevated temperatures and/or flame, reportedly creates a substantially continuous protective film generally encapsulating and/or enveloping the surface of the article onto which it is applied. The film-forming materials are based upon an aqueous latex dispersion of polyvinylchloride-acrylic copolymer, which is inherently fire-retardant.
Other disclosures which offer additional background information on flame-retardant materials include U.S. Pat. No. 4,776,854 entitled, “Method for Flameproofing Cellulosic Fibrous Materials”; U.S. Pat. No. 5,051,110 entitled, “Fibrous Material”; U.S. Pat. No. 5,695,528 entitled, “Treating Agent for Cellulosic Textile Material and Process for Treating Cellulosic Textile Material”; and U.S. Pat. No. 6,309,565 entitled, “Formaldehyde-Free Flame Retardant Treatment for Cellulose-Containing Materials”.